We had a crack in the bottom of the oven from left to right along the entire length - even ants crawled out of it! I applied the cement as directed with a metal spatula, allowed a few days for it to fully set, then lit the fires as usual. It seems to me that it worked exactly as I expected. Initially the color is dark gray, but after you have fire and it solidifies and forms a layer of ash, the color becomes light gray. It matches our concrete floor almost perfectly - we don't even notice the color difference.